Process of treating iron ores



Patented Dec. 25, 1928.

UNITED STATES 1,696,188 PATENT OFFICE.

THOMAS P. CAMPBELL, OF DENVER, COLORADO.

PROCESS OF TREATING IRON ORES.

No Drawing. Application filed May 19,

This invention relates to improvements in methods for the separation of the ferrous from the nonferrous materials in which the iron and some other metal such as Ti, Zn, Cu, etc, are chemically associated or in molecular compounds as distinguished from mechanical or physical association.

The separation of the ferrous from the nonferrous materials of the kind above referred to can be effected only by first breaking down the mechanical structure.

I am aware that it has been proposed to reduce the iron to sponge by heating the compound with a reducing agent such as hydrogen, carbon, carbon monoxide, sulphur, etc., at a high temperature, which, however, must be below the melting point of the metal as any fusion or sintering must be avoided. After the iron has been reduced to sponge, the chemical properties are taken advantage of to effect a separation. For example, the material is subjected to the action of a'solvent that will dissolve the sponge iron but which will not attack the remaining constituents of the mass.

It is the object of this invention to effect a separation of the iron from the other constituents of the compounds in which it is embodied by physical means as distinguished from the chemical means above described.

In the case of ferrous tita-nate, FeO, T iO if the iron is reduced to metallic orelementary form, or if it be first reduced and then reoxidized to a higher oxide, Fe O or Fe O the original compound is broken, and the two constituents may then be separated by pure- 1y physical means. v

In the carrying out of the method to which this application has reference, the preliminary treatment of the ore, before reduction, is also of prime importance. Microscopic examination of the ore in any given case shows that there is a definite degree of comminution to which the ore can be carried which will unlock the mineral aggregates from each other, but. which will not'break down the aggregates as such. Thus, in the case of certain titaniferous magnetite ore, the largest ilmenite grains are seen ,to be about three sixteenths of an inch in diameter. If this ore, therefore, be ground carefully to about one-quarter inch size, no fracturing of the ilmenite will take place.

The importance of taking particular care in the preliminary grinding lies in the fact that it is easier to break down, and separate,

1927. Serial No. 192,804.

the reduced, or reoxidized materials when the original aggregates have been as little disturbed as possible. This follows from the fact that reduced iron is soft and comparatively malleable; thus a grain of ilmenite which has been reduced to iron and titania will, on consequent grinding or comminution, respond differentially to the operation; that is, the soft iron and the hard titania will be mechanically split away from each other by virtue of their differences in hardness, mal leability, brittleness, etc.

This invention differs from the chemical process above referred to in several particulars. The iron compounds are treated to break up the chemical or molecular structure, but not primarily to obtain sponge, or metal lic iron. The object of this step is to confer upon the various constituents of the ore properties which makes possible a separation of these constituents by merely physical means. In the process to which I have made reference the sole object is to convert the iron into sponge'so as to render itsoluble in media which will not attack the titania. The success of this physical treatment is largely dependent upon the degree of comminution to which the ore is subjected before furnacing. The degree of comminution must besuch as to unlock the mineral aggregates from each other, but not such as to break up these aggregates assuch. By this step it is obviously impossible to attain theoretical unlocking, because the aggregates are not uniform in size; but it has been found that if the grinding is carried out so as to avoid breaking the largest grains, the natural fracture properties of the minerals will allow the grains of smaller size to be unlocked to a major extent.

I desire to particularly emphasize that for the purpose of this invention it is not essential that the iron shall be completely reduced to metallic iron, although such a reduction may beutilized. If the iron is reduced to metallic iron, it may be reoxidized to a higher or a lower oxide than that found in the ore. For example, in the case of llmenlte, we may reduce the ore to 1I0I1 1n the manner In the case of the so-called zinc ferrites, I

the zinc iron compound may be broken down without complete reduction to iron by heating the compound in a reducing atmosphere to a temperature above 450 degrees centigrade, for example,

3Fe O .ZnO CO 2Fe O, ZnO C0,;

Fe O .ZnO CO QFeO ZnO CO depending upon conditions imposed.

In order to more clearly explain the method I will now describe an actual operation.

A sample of titaniferous magnetite ore containing approximately 40.2% ilmenite, 49.8% magnetite, and gangue, was treated as follows: The ore was ground to pass a one-quarter inch screen and was then thoroughly mixed with of its weight in lignite coal of about the same size. This mixture was then fed into a rotary kiln type furnace which was heated, by heat externally applied, to a temperature of about one thousand degrees centigrade. During the passage of this mixture through the furnace a stream of live steam was passed through the furnace in the opposite direction. The rate at which the ore was passed through the furnace was such that there was sufiicient time for the desired reactions to take place. In this test the time of treatment was about 4.5 hours.

In this method the steam first reacts with the carbon of the coal to produce water gas (C+H. .O= C0 2H). This gaseous mixture then reacts with the iron compounds to reduce them to iron sponge. When the iron sponge comes into contact with the fresh live steam at the discharge end of the furnace, the iron is reoxidized to the magnetic oxide in accordance with the Formula 2 given above. During this 'reaction hydrogen is liberated and this aids in the reduction of the ore thereby making it possible, in continuous operation, to decrease the amount of carbonaceous material required to effect the reduction. It is desirable that there shall be little or no excess of carbonaceous material as an excess of such material hinders the reoxidation of the iron sponge.

After the iron ore had been passed through he furnace where it was first reduced to iron sponge and then reoxidized, it was passed once over a magnetic separator where the remaining coal, the ash and some gangue was removed. The magnetic oxide as well as any unoxidized iron sponge was then ground to pass a mesh screen after which it was again passed over the magnetic separator. This regrinding unlocked the magnetic oxide from the unreduced titania so that a satisfactory separation of the two was effected.

The degree of the first grinding, the furnacing treatment and the subsequent treatment of the furnace products must, of course. be varied somewhat with different ores, but in general the object is the same, namely, to break down the chemical compounds of the ore and to produce conditions which make the treated ore amenable to physical separation of its constituents.

It is possible to grind the ore fine before roasting but it is more economical to first coarse grind the material, then roast it and after it has been passed over the magnetic separator the first time, fine grind it.

Having thus described my invention what I claim as new is:

1. The process of treating ores containing iron, consisting of reducing comminuted ore to convert the iron into sponge, partially reoxidizing the iron sponge and then passing the mixture'over a magnetic separator.

2. The process of treating ores containing iron consisting of coarse grinding the ore, subjecting the ore to a reducing action whereby the iron is reduced to sponge, partially reoxidizing the iron sponge, subjecting the material to the separating action of a magnetic separator, regrinding the magnetic portion and subjecting the rcground material to the separating action of a magnetic separator.

3. The process of treating ores containing iron consisting of reducing the comminutcd ore to convert the iron into sponge, but with- .out fusing or sintering, partially reoxidizing the iron sponge, subjecting the material to a separating action by a magnetic separator, re grinding the magnetic material and subjecting the rcground material to a separating action in a magnetic separator.

l. The process of treating titaniferous ore containing iron, consisting in coarse grinding the ore, reducing the comminutcd ore to convert the iron into sponge, but without fusion or sintering, partially reoxidizing the iron sponge, subjecting the material thus treated to the separating action of a magnetic separator, whereby the magnetic portions are separated from the nonmagnetic, subjecting the magnetic materials to a. regrinding operation whereby they are reduced to such size that they will pass a sixty-five mesh screen and then subjecting the rcground particles to the separating action of a magnetic separator.

In testimony. whereof I affix my signature.

THOMAS P. CAMPBELL. 

